noreturn

noreturn is the type of:

  • break
  • continue
  • return
  • unreachable
  • while (true) {}

When resolving types together, such as if clauses or switch prongs, the noreturn type is compatible with every other type. Consider:

test.zig

  1. fn foo(condition: bool, b: u32) void {
  2.     const a = if (condition) b else return;
  3.     @panic("do something with a");
  4. }
  5. test "noreturn" {
  6.     foo(false, 1);
  7. }
  1. $ zig test test.zig
  2. 1/1 test "noreturn"...OK
  3. All 1 tests passed.

Another use case for noreturn is the exit function:

test.zig

  1. pub extern "kernel32" fn ExitProcess(exit_code: c_uint) callconv(.Stdcall) noreturn;
  3. test "foo" {
  4.     const value = bar() catch ExitProcess(1);
  5.     assert(value == 1234);
  6. }
  8. fn bar() anyerror!u32 {
  9.     return 1234;
  10. }
  12. const assert = @import("std").debug.assert;
  1. $ zig test test.zig -target x86_64-windows
  2. Created /deps/zig/zig-cache/o/_I6hZMbZvC3tMTV1FwcUPpThS8tQ8yAAJ2aGq_TjkmaXTVCTeUUEG_vmnEaqFNAL/test.exe but skipping execution because it is non-native.